# condition-based-waiting

> Use when tests have race conditions, timing dependencies, or inconsistent pass/fail behavior - replaces arbitrary timeouts with condition polling

- Author: Vitaly D.
- Repository: timequity/plugins
- Version: 20251210174826
- Stars: 3
- Forks: 0
- Last Updated: 2026-02-07
- Source: https://github.com/timequity/plugins
- Web: https://mule.run/skillshub/@@timequity/plugins~condition-based-waiting:20251210174826

---

---
name: condition-based-waiting
description: Use when tests have race conditions, timing dependencies, or inconsistent pass/fail behavior - replaces arbitrary timeouts with condition polling
---

# Condition-Based Waiting

## Overview

Flaky tests often guess at timing with arbitrary delays. This creates race conditions where tests pass on fast machines but fail under load or in CI.

**Core principle:** Wait for the actual condition you care about, not a guess about how long it takes.

## When to Use

- Tests have arbitrary delays (`setTimeout`, `sleep`)
- Tests are flaky (pass sometimes, fail under load)
- Tests timeout when run in parallel
- Waiting for async operations to complete

**Don't use when:**
- Testing actual timing behavior (debounce, throttle)
- Always document WHY if using arbitrary timeout

## Core Pattern

```typescript
// ❌ BEFORE: Guessing at timing
await new Promise(r => setTimeout(r, 50));
const result = getResult();
expect(result).toBeDefined();

// ✅ AFTER: Waiting for condition
await waitFor(() => getResult() !== undefined);
const result = getResult();
expect(result).toBeDefined();
```

## Quick Patterns

| Scenario | Pattern |
|----------|---------|
| Wait for event | `waitFor(() => events.find(e => e.type === 'DONE'))` |
| Wait for state | `waitFor(() => machine.state === 'ready')` |
| Wait for count | `waitFor(() => items.length >= 5)` |
| Wait for file | `waitFor(() => fs.existsSync(path))` |
| Complex condition | `waitFor(() => obj.ready && obj.value > 10)` |

## Implementation

```typescript
async function waitFor<T>(
  condition: () => T | undefined | null | false,
  description: string,
  timeoutMs = 5000
): Promise<T> {
  const startTime = Date.now();

  while (true) {
    const result = condition();
    if (result) return result;

    if (Date.now() - startTime > timeoutMs) {
      throw new Error(`Timeout waiting for ${description} after ${timeoutMs}ms`);
    }

    await new Promise(r => setTimeout(r, 10)); // Poll every 10ms
  }
}
```

## Common Mistakes

**❌ Polling too fast:** `setTimeout(check, 1)` - wastes CPU
**✅ Fix:** Poll every 10ms

**❌ No timeout:** Loop forever if condition never met
**✅ Fix:** Always include timeout with clear error

**❌ Stale data:** Cache state before loop
**✅ Fix:** Call getter inside loop for fresh data

## When Arbitrary Timeout IS Correct

```typescript
// Tool ticks every 100ms - need 2 ticks to verify partial output
await waitForEvent(manager, 'TOOL_STARTED'); // First: wait for condition
await new Promise(r => setTimeout(r, 200));   // Then: wait for timed behavior
// 200ms = 2 ticks at 100ms intervals - documented and justified
```

**Requirements:**
1. First wait for triggering condition
2. Based on known timing (not guessing)
3. Comment explaining WHY

## React Testing Library

For React tests, use built-in utilities:

```typescript
import { waitFor, screen } from '@testing-library/react';

// ✅ Wait for element
await waitFor(() => {
  expect(screen.getByText('Loaded')).toBeInTheDocument();
});

// ✅ Find (waits automatically)
const button = await screen.findByRole('button', { name: 'Submit' });
```

## Integration

**Complementary skills:**
- **systematic-debugging** - Replace timeouts identified in Phase 2
- **testing-anti-patterns** - Flaky tests often caused by timing guesses
- **testing** - General testing best practices